Tube Driver & BK Butler ?

[Walking Eagle]

In the schematic that I have of the blue tube, as in the driver tube, between the second Op-Amp and the first triode there are, in series: a 10nF capacitor and two resistors to 10K. The signal that goes on the grid is taken at the connection point between the two resistors. From your pedal you can understand how the resistor is placed from 100K?

[David Schwab]

In the schematic that I have of the blue tube, as in the driver tube, between the second Op-Amp and the first triode there are, in series: a 10nF capacitor and two resistors to 10K. The signal that goes on the grid is taken at the connection point between the two resistors. From your pedal you can understand how the resistor is placed from 100K?

From the schematic of both pedals that I have, this is about the only difference I see:

Here's the TubeWorks "Real Tube" RT-901:



Here's the Blue Tube RT-903:



That 100K resistor is reducing the level into the tube, which is why the Blue Tube has less distortion than the Tube Driver. It was still too much for me, so I replaced the tube with a 12AU7, since that has less gain than a 12AX7.

I know they had different models, so maybe you are looking at a different schematic.

[Walking Eagle]

“It has a TL072. The TL072 is a J–FET input op amp. The JRC4558 has a bipolar front end. I find the TL0s tend to sound brighter.”….
therefore you prefer the sound of the TL072, I understand you correctly?
On the'RT-903 the divider 100K + 10K makes sure that on the grid triode arrivals the first one-tenth of the swing voltage delivered from Op-Amp (the second resistor 10K acts as a grid-stopper).
On the'RT-901, as usual, the voltage divider consists of two 10K resistors, then the swing that pilot the first grid has half the amplitude of the dispensed from Op-Amp.
It seems an excessive difference however (1/10 VS ½ Vpp), between the two situations, even if on the RT-903 is used 12AX7.
In my prototype, 10K + 10K combination makes the 12AU7 voicing as a deep and hot, but light (smooth) overdrive… than I do not think so interesting to experience what would happen with 100K + 10K!
It seems to me that there are numerous errors in these two schematics that you have shown: in both, between the pins 6 and 7 oh the Op-Amp, in parallel with the 500K pot is indicated a 12pF capacitor alone (in my opinion it is 120pF...); on the RT-901 one of the two 10K resistors seem badly positioned (the “horizontal” resistor should not be connected as a grid stopper, between grid and node, but between the node and capacitor 47nF).
In the schematics that I have and in the prototype that we are experiencing, this 47nF is substitute by 10nF and seems to go really well.
I will try to replace it with others, for example 22nF.

[David Schwab]

therefore you prefer the sound of the TL072, I understand you correctly?

I haven't tried any other op ams in there, but I also see no reason to do so. Also the TL072 has a nice high impedance input. I'm looking for a warm clean tone, not over drive. Why would I want a darker sounding op amp?

On the'RT-903 the divider 100K + 10K makes sure that on the grid triode arrivals the first one-tenth of the swing voltage delivered from Op-Amp (the second resistor 10K acts as a grid-stopper).
On the'RT-901, as usual, the voltage divider consists of two 10K resistors, then the swing that pilot the first grid has half the amplitude of the dispensed from Op-Amp.
It seems an excessive difference however (1/10 VS ½ Vpp), between the two situations, even if on the RT-903 is used 12AX7.
In my prototype, 10K + 10K combination makes the 12AU7 voicing as a deep and hot, but light (smooth) overdrive… than I do not think so interesting to experience what would happen with 100K + 10K!
It seems to me that there are numerous errors in these two schematics that you have shown: in both, between the pins 6 and 7 oh the Op-Amp, in parallel with the 500K pot is indicated a 12pF capacitor alone (in my opinion it is 120pF...); on the RT-901 one of the two 10K resistors seem badly positioned (the “horizontal” resistor should not be connected as a grid stopper, between grid and node, but between the node and capacitor 47nF).
In the schematics that I have and in the prototype that we are experiencing, this 47nF is substitute by 10nF and seems to go really well.
I will try to replace it with others, for example 22nF.

You probably have the later revision schematics. Also, the schematics by JD Sleep are said to have errors, or are different. The ones I posted are from TubeWorks. I haven't checked mine against the schematics, but my pedal is a one of the early ones when they first came on the market in '89.

If you Google it, a lot of people have hum problems with these pedals.

The BlueTube was marketed as a "tube enhancer", not an overdrive. The 100k series resistance reduces the level of the signal going to the tube, so the tube is not driven as hard. The idea was to keep it clean. This pedal was meant for bass and keyboards, or for guitar players looking for cleaner tube tones.



I use it with bass. I'm not using it for distortion, and usually have it set crystal clear. Sometimes I use it for a little grit. But mostly it's used to fatten up the tone, which is what it was designed for.

The problem with the pedal is the output is not buffered. So in most situations the pedal has lower output than is needed if you don't want to over drive the 12AX7. To get the pedal up to unity gain required the drive control to be cranked up, which made the pedal distort more than I wanted. So using a 12AU7 is a common way to clean up the tone of amps. I own a Mesa 400+, and this is also a common mod for that amp. The 12AX7 has gain factor of 100, while the 12AU7 is 19.

So one of the things I was originally going to do was build a JFET based buffer with gain for the output, and then I could turn down the drive control to get cleaner sounds. When I tired this out with bread boarded circuits, the 12AX7 was still too hot. The 12AU7 works perfectly in this context, and I can still get the tone VERY fuzzy if I need it. I can cop the perfect Jack Bruce tone with ease.

So at some point I'm going to add an output buffer, and also see if I can get rid of the hum.

[Walking Eagle]

To obtain a larger signal output by the Blue Tube you could match it with a good booster. As for the hum, I fear that in a small container so it is virtually impossible to eliminate it, wanting to keep us inside the transformer.
As for the output buffer would indicate you a JFET circuit I have already successfully tested in different contexts, and also tends to warm the sound. Just enough time to scan the schematic ...

[David Schwab]

To obtain a larger signal output by the Blue Tube you could match it with a good booster. As for the hum, I fear that in a small container so it is virtually impossible to eliminate it, wanting to keep us inside the transformer.
As for the output buffer would indicate you a JFET circuit I have already successfully tested in different contexts, and also tends to warm the sound. Just enough time to scan the schematic ...

Yeah, I was going to use a JFET buffer.

There are threads on other forums where apparently the owners of Blue Tubes have removed the transformer from the case, and also used tube shields and the like, and have not eliminated the hum. It's only present when the tube is in the circuit, and mine is not as loud as some people report.

I had a gig this past weekend and my Blue Tube was DOA! Usually that means the tube became lose in the socket, but that wasn't the case this time. I got it working only to have it stop making sound again. So I'm going to have to look it over to see where the problem is. Might be time to leave it home and build a replacement.

[Walking Eagle]

Keep the transformer and the power supply circuit by the circuit that processes the signal is often not sufficient.
In my experience, I learned that it is necessary to filter well the tensions that fuel circuits, both tube and solid state that this is also true for the signal tube filaments (such as our small NOVAL).
On the picture of my avatar you see the two heat sink that mounting the uA7806’s that fueled the filaments of the two 12AU7 (Philips JAN 5814A) of the front end stage (parallel SRPP directly connected to the grid of the 300B, its filament was powered by a LM338K mounted on the rear). And it was a power stage, not signal...
In the prototype of my two-valve version of the Tube Driver ALL voltages are thoroughly filtered and then adjusted using IC's. And I can say I achieved a very good result, although the size stomp boxes will necessarily larger than usual... I do not want to apply a output buffer to my overdrive, but I suggest you try this schematic because in other applications it gave me great results (especially when the jack that connects the pedal to the amplifier is long).

[Walking Eagle]

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